Vedran Čačić <ved...@gmail.com> added the comment:

Sorry, I think you still don't understand.

The emulation of double dispatch by single dispatch, with all complications it 
brings, is the only reason NotImplemented exists. If Python didn't have binary 
operators (or inheritance), I'm quite sure it wouldn't have NotImplemented. The 
idea was never "oh, this method isn't supported", but much more precise "this 
half of protocol, with given ordering of operands according to a class 
hierarchy, isn't implemented - try the other half".

Of course, you might argue that _once Python has NotImplemented_, it can be 
used elsewhere - but as I said, I don't think it should be encouraged.

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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue37934>
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